Hi Steve,
With respect, I was almost as surprised to read your comments about aluminium oxide, as I was when I received delivery of my Taig Micromill.
When I ordered the mill, I had done very little research, having been blinded by the thoughts of extending my CAD facilities with CAM. I sold the mill several years ago when I also disposed of my other workshop machinery. Therefore, I’m not really in a good position to comment about the mill’s sliding surfaces.
However, having come up through a six-year toolmaking apprenticeship commencing in 1950, and an ongoing contact with machine tools since then, it took a relatively new way of thinking when using the mill with its major components made from extruded and anodised aluminium. Upon reflection, I suppose that the forces required to accelerate the table in the X and Y directions would be less. Arguably beneficial in terms of small stepper motors which could lose their place through slippage.
As for aluminium oxide, in those early days when I entered the fray, it was common practice with company-issued pint pots, to initial their ownership by scratching through the glazed pottery with a piece of aluminium. This practice would also leave a black(ish), relatively indelible, deposit.
Also of significance was the fact that the vast majority of grinding wheels were aluminium oxide. (I can’t recall seeing more than one or two diamond grinding wheels.)
May I suggest a quick look at Mohs' Hardness scale which indicates that diamond gives a reading of 10, while aluminium oxide is close behind with a reading of 9.
In terms of lapping, honing, or scraping – once the (anodised) oxide layer has been removed, I would consider that a sliding surface would be well and truly stuffed. Try rubbing two bits of (clean) aluminium together and see what happens. It's quite galling
Best regards,
Sam
Edited By Sam Stones on 26/06/2012 23:46:45